$$2(a^{2}+ab)+3-ab; =a-3; =b=5$$
$a=b+3\text{, }b=-\frac{\sqrt{12c-27}}{6}-\frac{5}{2}\text{, }c\in \mathrm{C}$
$a=b+3\text{, }b=\frac{\sqrt{12c-27}}{6}-\frac{5}{2}\text{, }c\in \mathrm{C}$
$a=b+3\text{, }b=-\frac{\sqrt{12c-27}}{6}-\frac{5}{2}\text{, }c\geq \frac{9}{4}$
$a=b+3\text{, }b=\frac{\sqrt{12c-27}}{6}-\frac{5}{2}\text{, }c\geq \frac{9}{4}$
